1. Field of the Invention
This invention relates to a process and apparatus for making multiple copies, and more particularly, to a multiple reproduction process and apparatus in which a toner image formed by an electrophotographic technique is transferred onto and temporarily fixed to an image retention medium in order to carry out a multiple reproduction or printing operation with high efficiency.
2. Description of the Prior Art
It is often desired to make multiple copies from a single original. The customary electrophotographic process may be repetitively applied for this purpose, but this is not advantageous, especially for a large number of copies, because it requires the expenditure of a relatively large amount of time per copy. One conventional technique, which is widely used these days, to cope with this problem is to make a master plate with the application of an electrophotographic process and then to set this master plate in an offset printing machine, thereby implementing a multiple reproduction operation. This technique presents some improvements since it does not require the repetitive application of an electrophotographic process in making multiple copies. However, this technique still suffers from various disadvantages. For example, in accordance with this technique, making of a master plate and multiple printing are two separate operations, which requires the provision of two separate machines, i.e., an electrophotographic machine for making a master plate and an offset printing machine for making multiple copies. Therefore, it is disadvantageous because it occupies an unnecessarily large space for installation of the machines. Another disadvantage is the cumbersomeness in making and setting a master plate as a preparatory step for multiple reproductions. This technique is also economically disadvantageous because a master plate is discarded after use and it is not used repetitively.
Another conventional technique is to use the silver salt process, or silverprint method in making a master plate instead of an electrophotographic process. It is true that a master plate provided by this technique has a higher abrasive-resistance property and an image formed on the master plate is better in quality. However, as easily understood, this technique is no more advantageous than the one described above. Moreover, a master plate to be made in accordance with this technique is more expensive, and the handling of the master plate is more cumbersome because it is photosensitive.
Still another conventional technique is the use of a master paper having thereon a silicon resin layer. That is, in accordance with this technique, a toner image is first formed on a ZnO paper. Then the toner image together with the ZnO layer is transferred onto a master paper with the application of heat. The thus formed master paper is used for multiple reproductions with the use of a hydrophilic ink. The cost of this technique is prohibitive since it requires the preparation of ZnO paper as well as master paper. It will be easily understood that the principle of this technique is not much different from the other prior art methods as discussed above.
Meanwhile, Buchan et al. U.S. Pat. No. 3,923,392 issued Dec. 2, 1975 suggests another approach in making multiple copies. In this patent, there is shown an electrophotographic copier which includes a transfer and fusing system and a paper transport system. These systems are operatively associated with the rotation of a photoconductive drum. Thus, an electrostatic latent image formed on the surface of the photoconductive drum is developed by a unique developing unit and, then, the developed image is transferred to an elastomeric transfer belt. Thereafter, the image on the transfer belt is subjected to radiant heat and then finally transferred onto a copy paper. It is to be noted, however, that the transfer belt is always kept in contact with the photoconductive drum. Therefore, in making multiple copies, the latent image still remaining on the photoconductive drum must be developed and the developed image must be transferred to the transfer belt. However, since the latent image decays with respect to time and it deteriorates because of its use, the bias voltage at the developing unit must be increased for compensation. Or, another exposure might have to be carried out after making several copies because of the severe deterioration of the latent image. This conventional technique is also disadvantageous from a energy-saving viewpoint since the photosensitive drum must be kept rotating during the multiple reproduction operation.